Exemplary embodiments of the invention relate to a method for continuously clarifying a free-flowing suspension with a centrifuge.
German patent document DE 32 28 074 A1 discloses a method that advantageously permits control of a continuously emptying clarifying separator having a drum. A suspension parameter—here the level of turbidity of a clear phase running out of the drum—is determined and used to monitor the emptying of the solid-matter chamber of the drum. The solid-matter phase is emptied continuously. If the turbidity in the clear phase becomes too high, the clear phase is led back into the drum.
It is also known to use a clarifying separator for the clarification of liquids, in particular beverages, in which the solid matter is emptied discontinuously with the aid of a piston valve for opening and closing discharge openings if the level of turbidity, measured with the photocell, exceeds a certain limiting value.
This method has also proven worthwhile in specific applications. Unfortunately, there is solid matter that causes the photocell to become blind over time, so that in these cases satisfactory control of the separator is no longer ensured. There is therefore a need for simple and nevertheless most precise methods for determining a moment that is highly suitable for the emptying of solid matter during the clarification of suspensions of solid matter by using discontinuously automatically emptying separators.
Exemplary embodiments of the present invention provide a method for continuously clarifying a free-flowing suspension or a free-flowing product with a centrifuge, in particular a separator—an automatically emptying separator—that discontinuously automatically empties solid matter and comprises a rotatable drum having a vertical axis of rotation, having an inlet for the suspension to be clarified and at least one liquid discharge for the continuous discharge of at least one clarified liquid phase and solid-matter discharge openings that are to be opened discontinuously for the discontinuous discharge of the solid phase. The method involves: a) measuring one or more of the suspension parameters comprising mass, mass of solid matter in suspension, mass flow, temperature, density, cumulative density; and b) initiating a time-limited solid-matter discharge as a result of a repeated determination according to step b) upon reaching or after exceeding a limiting value dependent on one or more of the measured suspension parameters.
The limiting value can be one that can be (preferably) determined directly from the behavior over time of the one or more suspension parameters. However, it can also be a limiting value that can be determined from the first (or second or nth) derivative of the behavior over time of the one or more suspension parameters, for example in the form of a differential ratio of the measured values of the suspension parameter and the time intervals between the measurements of the suspension parameter.
The direct or indirect determination of one or two or more of the aforementioned parameters makes it possible to determine the mass of solid matter (or value proportional thereto) in each case that has been separated from the suspension since the last emptying, in order to draw conclusions about the level of filling of the solid-matter chamber with solid matter separated out from the suspension, which has collected in the solid-matter collecting chamber. In particular, the solid matter must not reach the edge of the disk stack. If, therefore, the mass of solid matter value determined exceeds a predefined limiting value—for example determined during trial operation—emptying is initiated in order to empty the solid-matter collecting chamber entirely of solid matter or in any case to the greatest possible extent.
To determine the suspension and/or mass of solid matter, a Coriolis flowmeter is in particular suitable, with which a sufficiently accurate determination of this value or these values is possible in a straightforward manner. The Coriolis flowmeter is preferably designed to measure the mass flow, the density and the cumulative density in parallel. It preferably also measures the temperature. Cumulative density means that the density is measured again and again at time intervals, that the sum of these values is formed (directly or suitably processed further, e.g. multiplied by the time interval between the measurements) and thus a value directly corresponding to the mass of solid matter is determined.
If the suspension to be processed has a relatively uniform, constant proportion of solid matter, it may be sufficient for the mass determination to determine the mass flow per unit time of incoming suspension and to integrate the same over time, in particular by means of addition, in order therefrom to determine by computation the proportion of solid matter that has collected in the solid-matter collecting chamber. However, if the proportion fluctuates, it may be necessary, with the aid of a previously stored table—e.g. determined in trials—or with the aid of a previously determined functional relationship and the measurement of a further suspension parameter such as the density, to determine in each case how high the proportion of solid matter in the incoming suspension is at present, which is possible with modern Coriolis flowmeters. With an additional temperature determination, which the Coriolis flowmeter can preferably likewise also carry out in an integrated manner, and with a supplementary accumulation of the measured values—which is preferably likewise carried out directly by the Coriolis flowmeter/sensor, the level of filling of the solid-matter collecting chamber of the drum can be determined.
At the same time, the Coriolis flowmeter (Coriolis meter) can be used to protect the automatically emptying separator or the drum thereof against excessively high densities in the inlet, by the inlet being prevented (e.g. by controlling a valve) when the maximum permissible density for the respective automatically emptying separator is exceeded. This value is previously known and identified for each separator.
The individual method steps do not necessarily have to be carried out in a structural unit of the separator but can also be carried out by external devices (in particular measuring devices, sensors, control unit, individually or in combination therewith and possibly further devices).